This is proposal to conduct a pathologic review and reclassification of biopsies for benign breast lesions performed between 1930-1982 on over 1800 patients. These cases have been clinic patients and private patients of one surgeon at The Presbyterian Hospital in the City of New York at Columbia- Presbyterian Medical Center. They are epithelial, primarily proliferative cases which have been the subject of previous research, and for which an average of 20 years of follow-up has been recorded, with over 160 carcinomas known to date. The primary purpose of this study is to assess the risk of breast cancer associated with the various histologically defined characteristics of benign proliferative breast lesions, and to estimate the extent to which these risks are modified by characteristics about these patients, such as positive family history of breast cancer, parity, age at first birth, multiple breast biopsies and aspirations, elapsed time after biopsy, and advancing age. It is of particular interest to compare the effects of atypical hyperplasia and a positive family history of breast cancer with those reported in other cohorts. A long-term goal of this study is to add to an understanding of the etiology of breast cancer. An immediate goal is to increase knowledge about risk factors for breast cancer in order to help identify women who are at increased risk and therefore especially stand to benefit from screening for early detection.